Okay so i just bought a 2006 KX250F for a motor cycle shop. I started riding the bike and the backfire wasnt bad when it was warming up but after it was warmed up in iddle it still had backfire. and when i ride it easy it has backfire to it too. so i took it to the shop i bought it from said there was nothing wrong and it so post to do it. So is that true because i thought there wasnt so post to be any backfire unless you get in the high rpms.